Solar phenomena

Throughout history, observation technology and methodology advanced, and in the 20th century, interest in astrophysics surged and many solar telescopes were constructed.

The remaining 1.69% (equal to 5,600 times the mass of Earth) consists of heavier elements, including oxygen, carbon, neon and iron.

[7] The Sun formed about 4.567 billion[a][8] years ago from the gravitational collapse of a region within a large molecular cloud.

Most of the matter gathered in the center, while the rest flattened into an orbiting disk that became the balance of the Solar System.

The central mass became increasingly hot and dense, eventually initiating thermonuclear fusion in its core.

The Sun is a G-type main-sequence star (G2V) based on spectral class, and it is informally designated as a yellow dwarf because its visible radiation is most intense in the yellow-green portion of the spectrum.

It is actually white, but from the Earth's surface, it appears yellow because of atmospheric scattering of blue light.

Most ejections originate from active regions on the Sun's surface, such as sunspot groupings associated with frequent flares.

This rearrangement is accompanied with a sudden release of energy stored in the original oppositely directed fields.

These particles can impact the Earth's magnetosphere in the form of a geomagnetic storm and present radiation hazards to spacecraft and astronauts.

A prominence is a large, bright, gaseous feature extending outward from the Sun's surface, often in the shape of a loop.

A typical prominence extends over many thousands of kilometers; the largest on record was estimated at over 800,000 kilometres (500,000 mi) long [24] – roughly the solar radius.

Other prominences form huge loops or arching columns of glowing gases over sunspots that can reach heights of hundreds of thousands of kilometers.

The slow solar wind has a velocity of about 400 kilometres per second (250 mi/s), a temperature of 2×105 K and a composition that is a close match to the corona.

[35][36] Both the fast and slow solar winds can be interrupted by large, fast-moving bursts of plasma called interplanetary CMEs, or ICMEs.

The Sun can produce intense geomagnetic and proton storms capable of causing power outages, disruption or communications blackouts (including GPS systems) and temporary/permanent disabling of satellites and other spaceborne technology.

[39][40] An aurora is a natural light display in the sky, especially in the high latitude (Arctic and Antarctic) regions, in the form of a large circle around the pole.

It is caused by the collision of solar wind and charged magnetospheric particles with the high altitude atmosphere (thermosphere).

Most auroras occur in a band known as the auroral zone,[41][42] which is typically 3° to 6° wide in latitude and observed at 10° to 20° from the geomagnetic poles at all longitudes, but often most vividly around the spring and autumn equinoxes.

Collisions between these ions and the atmosphere release energy in the form of auroras appearing in large circles around the poles.

[44] The disturbance in the interplanetary medium that drives a storm may be due to a CME or a high speed stream (co-rotating interaction region or CIR)[45] of the solar wind originating from a region of weak magnetic field on the solar surface.

These include Solar Energetic Particle (SEP) events, geomagnetically induced currents (GIC), ionospheric disturbances that cause radio and radar scintillation, disruption of compass navigation and auroral displays at much lower latitudes than normal.

A 1989 geomagnetic storm energized ground induced currents that disrupted electric power distribution throughout most of the province of Quebec[46] and caused aurorae as far south as Texas.

[48] Geomagnetically induced currents are a manifestation at ground level of space weather, which affect the normal operation of long electrical conductor systems.

During space weather events, electric currents in the magnetosphere and ionosphere experience large variations, which manifest also in the Earth's magnetic field.

GIC can cause problems such as increased corrosion of pipeline steel and damaged high-voltage power transformers.

[50] One of these observers was the renowned astronomer Johannes Hevelius who recorded a number of sunspots from 1653 to 1679 in the early Maunder minimum, listed in the book Machina Coelestis (1679).

Around 1852, Sabine, Wolf, Gautier and von Lamont independently found a link between the solar cycle and geomagnetic activity.

[52] Carrington and Gustav Spörer discovered that the Sun exhibits differential rotation, and that the outer layer must be fluid.

[53] Other major achievements included understanding of:[54] In the later twentieth century, satellites began observing the Sun, providing many insights.